Forgot to add that when I enable the "Boot Up Floppy Seek" BIOS option, which I normally always leave disabled, I now get a "Floppy disk fail(40)" error. Pressing F1 and continue to boot it will give the same symptom as I described above. Normally that indicates no floppy drive or cable not connected correctly but that is not the case.

AFAIK it's the south bridge job, and it looks to be a BGA chip. Could be dying, could be cracked solder balls. Put the mobo on a flat surface and press the chip with your finger - see if that helps any. If there is a change in behaviour you need to reflow that BGA.

>Used multiple different floppy cables

that was my guess, try tracking floppy connector further and check continuity, maybe there is a crack somewhere along the way.

Deunan wrote on 2024-05-10, 17:08:

AFAIK it's the south bridge job, and it looks to be a BGA chip. Could be dying, could be cracked solder balls. Put the mobo on a flat surface and press the chip with your finger - see if that helps any. If there is a change in behaviour you need to reflow that BGA.

Just tried that but unfortunately that didn't change the behavior.

rasz_pl wrote on 2024-05-10, 17:29:

>Used multiple different floppy cables

that was my guess, try tracking floppy connector further and check continuity, maybe there is a crack somewhere along the way.

Going to do that tomorrow (if time permits). But had a good look already earlier when I did the repair work. So not to hopeful I will find anything new.

If BIOS shows floppy error only when seeking is enabled you can limit your search area quite a lot. All the BIOS does is step 43 times in and then out, checking the track 0 sensor output. This lets it detect 40-cylinder drives (360k). So the only signals used are drive select, motor on, direction, step and track 0 (that's input). Everything else doesn't matter.

BTW I never had it happen to me but it's possible for the floppy cables with twist to go bad at the twisted section (the cable is too thin and pressed to hard in factory, wires break inside). Try straight cable or the non-twisted connector and either set the drive to B: (if only to test) or there might be a drive letter swap option in BIOS.

Deunan wrote on 2024-05-11, 09:52:

If BIOS shows floppy error only when seeking is enabled you can limit your search area quite a lot. All the BIOS does is step 43 times in and then out, checking the track 0 sensor output. This lets it detect 40-cylinder drives (360k). So the only signals used are drive select, motor on, direction, step and track 0 (that's input). Everything else doesn't matter.

BTW I never had it happen to me but it's possible for the floppy cables with twist to go bad at the twisted section (the cable is too thin and pressed to hard in factory, wires break inside). Try straight cable or the non-twisted connector and either set the drive to B: (if only to test) or there might be a drive letter swap option in BIOS.

Found the issue. What I didn't test yet was to remove all cards (USB, network, sound cards). When I did that the floppy drive suddenly was working again. Then added them one by one and it seems the ISA sound card is causing this issue. Had to suspect this earlier as I had issues with sound suddenly not working when playing a game with an ALS100 card but thought it was a broken card. When replacing it with a ES1868F everything was working at first.

Sound card is still working correctly (with standard values IRQ5 A220 DMA1+DMA0). Only the floppy drive is not working anymore when the ES1868F card is inserted now. As the floppy drive is using IRQ6 and DMA2 there shouldn't be any resource conflicts.

So a bit puzzled at the moment. Anyone got an idea what could cause this? Will do a continuity/voltage test on the ISA slot tomorrow. But I have no idea how to measure the floppy connector on the motherboard though. So some hints (without oscilloscope) are appreciated.

Is this a sound card with extra IDE interface (for CD-ROM)? Is it disabled properly?

Deunan wrote on 2024-05-12, 15:32:

Is this a sound card with extra IDE interface (for CD-ROM)? Is it disabled properly?

Both the tested ASL100 and ES1868F have an extra IDE interface. I disabled them on both with their config tools.

Also just now measured the ISA connector and all voltages are within range. Also did a continuity test and so far everything seems ok.

*EDIT* Also added an ALS4000 PCI card (with IRQ5, DMA1, A220) and with that the floppy drive is also working. Didn't do a DOS sound test yet.

Forgot that I had a cheap oscilloscoop so took a look at the RDATA, MOTEA#, DRVSA pins on the floppy connector with and then without an ISA card. Unfortunately the signals are exactly the same. So I am out of ideas what the problem could be. So will be going with the ALS4000 PCI sound card for now. Not a bad DOS card at all but not what I had in mind.

So it doesn't work with either ISA card? But does work with PCI? Perhaps it's some sort of PnP issue, did you try manual assigment of the sound card IRQ/DMA to ISA in BIOS?
Or perhaps it's a some weird ISA slot problem, like maybe something got into one of the slots and is shorting DMA1 and DMA3 signals for example (or IRQ with either IRQ5 or IRQ7).

Deunan wrote on 2024-05-13, 13:10:

So it doesn't work with either ISA card? But does work with PCI? Perhaps it's some sort of PnP issue, did you try manual assigment of the sound card IRQ/DMA to ISA in BIOS?
Or perhaps it's a some weird ISA slot problem, like maybe something got into one of the slots and is shorting DMA1 and DMA3 signals for example (or IRQ with either IRQ5 or IRQ7).

I always do a manual reservation in the BIOS (if possible). Checked for shorts yesterday and took a good look as well. But no shorts are found. ISA socket is brand new and was soldered on the board as the motherboard lacks it normally. This mod has been done successfully before by other members on Vogons. I thought it was maybe a bad solder job but after intens investigation yesterday I can't find a problem. No shorts and voltage are in range.

Ah, so ISA slot was added later. I gave the photo another look, there's a few resistor packs near the ISA - are all of those populated on your mobo? I was wondering if there is perhaps a missing pull-up (or pull-down) for the IRQ or DRQ lines.
Another possibility is the BIOS, since it's not expecting to have ISA slot installed perhaps there are some internal chipset registers not set up correctly. This might be somehow affecting IRQ/DMA routing from the slot and the internally emulated floppy controller. It's a wild guess but I don't have other ideas.

Deunan wrote on 2024-05-13, 15:38:

Ah, so ISA slot was added later. I gave the photo another look, there's a few resistor packs near the ISA - are all of those populated on your mobo? I was wondering if there is perhaps a missing pull-up (or pull-down) for the IRQ or DRQ lines.
Another possibility is the BIOS, since it's not expecting to have ISA slot installed perhaps there are some internal chipset registers not set up correctly. This might be somehow affecting IRQ/DMA routing from the slot and the internally emulated floppy controller. It's a wild guess but I don't have other ideas.

It was working for a couple of weeks. So the BIOS supports it. Also other Vogons members used the standard BIOS.

I checked the motherboard before and all was there. But I didn't measure them so will do that in the future. For now I put it on the backlog as I am a little fed up with it. 😉